In-situ cap and method of fabricating same for an integrated circuit device

ABSTRACT

An in-situ cap for an integrated circuit device such as a micromachined device and a method of making such a cap by fabricating an integrated circuit element on a substrate; forming a support layer over the integrated circuit element and forming a cap structure in the support layer covering the integrated circuit element.

FIELD OF THE INVENTION

This invention relates to an in-situ cap for an integrated circuitdevice such as a micromachined device and to a method of making such anin-situ cap.

BACKGROUND OF THE INVENTION

Conventional caps for integrated circuit devices such as micromachineddevices are often used to protect and isolate. Typically the caps aremade independently of the device itself and then attached after thedevice fabrication is completed. Often the cap is fabricated fromsilicon and fastened to the devices with an organic adhesive or with aninorganic glass or metal. While this approach can be satisfactory, itdoes require separate processes to make the caps and then to join themto the integrated circuit devices. One set of joining processes appliescaps to integrated circuit devices before the wafers are singulated.This requires expensive wafer scale processes and equipment. Cap stresseffects can cause yield loss if the process is not tightly controlled.However, a tightly controlled wafer level process protects the delicatemicromachined devices early in the manufacturing process. Another set ofprocesses applies the caps after singulation. This can be simpler toimplement but it requires special precautions to avoid contaminationduring wafer singulation and other process steps. Still another approacheliminates the requirement for directly attaching caps to the integratedcircuit devices by mounting and wire bonding the devices inside cavitypackages. In essence, the next level package becomes the cap. Thismethod often utilizes expensive hermetically sealed ceramic or metalpackages. It also requires that the manufacturing facility maintainunusual cleanliness standards in order to avoid contamination duringassembly of the delicate micromachined devices.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide an improvedin-situ cap for integrated circuit devices including micromachineddevices and a method of making it.

It is a further object of this invention to provide such a cap andmethod which utilize the basic integrated circuit fabrication process tomake the cap as well.

It is a further object of this invention to provide such a cap andmethod which provides the cap as an integrated in-situ part of thedevice itself.

It is a further object of this invention to provide such a cap andmethod which require no special or independent effort to make or installthe cap.

It is a further object of this invention to provide such a cap andmethod in which the cap can be used to preserve a suitable environmentwithin the cap such as a gas or liquid fill or a vacuum.

It is a further object of this invention to provide such a cap andmethod which protects the capped device immediately upon completion ofthe processing before any further handling including die separation,testing and handling.

It is a further object of this invention to provide such a cap andmethod which has much lower manufacturing cost.

It is a further object of this invention to provide such a cap andmethod in which post-processing is made easier because the devices areless vulnerable since they are capped at the end of wafer processingbefore die cutting.

It is a further object of this invention to provide such a cap andmethod which requires the same low temperature processing as the rest ofthe integrated circuit.

The invention results from the realization that a truly improved, morerobust, simpler and less expensive in-situ cap for an integrated circuitdevice and method of making such a cap can be achieved by fabricating acap in-situ on an integrated circuit device as a part of the integratedcircuit fabrication process by forming a support layer on the integratedcircuit device and then forming the cap structure in the support layercovering the integrated circuit element.

This invention features a method of fabricating an in-situ cap for amicromachined device including fabricating a micromachined element on asubstrate with a sacrificial support layer intact and fabricating a capsacrificial support layer over the micromachined element. The capstructure is formed in the sacrificial layers covering the micromachinedelement and the sacrificial layers are removed within the cap structureto release the micromachined element leaving an in-situ cap integralwith the device.

In a preferred embodiment forming the cap structure may include forminga cap hole around the element. Forming the cap structure may alsoinclude filling the cap hole to form a cap wall and covering thesacrificial layers to form a top connected with the cap wall. The capmay be formed with at least one hole and removing the sacrificial layersmay include introducing a release agent through the hole in the cap. Thesubstrate may be formed with at least one hole and removing thesacrificial layers may include introducing release agent through thehole in the substrate. The cap hole may be closed to seal the cap. Afluid filler may be introduced through the cap hole into the capsurrounding the micromachined element. The cap hole may be closed toseal in the fluid. The cap hole may be small and the surface tension ofthe fluid may prevent its escape. Fabricating a cap may include forminga contact on the cap. The micromachined element may include a switch andthe contact may be a terminal of the switch. Fabricating a cap may alsoinclude forming a gate electrode on the cap for operating the switch.The fluid may be a crosslinkable material; the volume in the cap may bea vacuum; the fluid may modify a surface inside the cap.

This invention also features a method of fabricating an in-situ cap foran integrated circuit device including fabricating an integrated circuitelement on a substrate, forming a support layer over the integratedcircuit element and forming a cap structure in the support layercovering the integrated circuit element.

In a preferred embodiment the method may further include removing thesupport layer within the cap structure.

This invention also features a micromachined device with an in-situ capincluding a substrate, a micromachined element on the substrate and anin-situ cap integral with the substrate and covering the element. Thereis at least one conductor extending from the element under the capthrough the substrate to an external terminal.

In a preferred embodiment, the cap may be filled with liquid; the liquidmay be a dielectric. The micromachined element may include a switch; thecap may include a hole; the micromachined element may include an opticaldevice; and the hole may be an optical port. The cap may include acontact; the micromachined element may include a switch; and the contactmay be a terminal of the switch. The cap may include a gate electrodefor operating the switch.

This invention also features a micromachined device with an in-situ capincluding a substrate, a micromachined element on the substrate, and anin-situ cap integral with the substrate covering the element. Themicromachined element may be an optical device and there may be anoptical port for accessing the optical device. In a preferredembodiment, the port may be in the cap.

This invention also features a micromachined device with an in-situ capincluding a substrate, a micromachined element on the substrate, and anin-situ cap integral with substrate and covering the element. There maybe a liquid disposed in the cap.

In a preferred embodiment the liquid may be a dielectric.

This invention also features an integrated circuit device with anin-situ cap including a substrate, an integrated circuit element on thesubstrate, and an in-situ cap integral with the substrate and coveringthe element. At least one conductor may extend from the element underthe cap through the substrate to an external terminal.

This invention also features an integrated circuit device with anin-situ cap including a substrate, an integrated circuit element on thesubstrate, and an in-situ cap integral with the substrate and coveringthe element. The integrated circuit element may be an optical device andthere may be an optical port for accessing the optical device.

This invention also features an integrated circuit device with anin-situ cap including a substrate, an integrated circuit element on thesubstrate, and an in-situ cap integral with the substrate and coveringthe element. A liquid may be disposed in the cap.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a schematic side elevational sectional diagram of anintegrated circuit device, namely a micromachined device, as it appearsduring the method of this invention just prior to release of thesacrificial support layers in the cap;

FIG. 2 is a view similar to FIG. 1 after the release of the sacrificialsupport layer showing the device with in-situ cap according to thisinvention;

FIG. 3 is a view similar to FIG. 1 in which the micromachined switchelement includes an additional terminal and counter gate on the cap;

FIG. 4 is a view similar to FIG. 2 of the device of FIG. 3;

FIG. 5 is a schematic side elevational sectional view of a micromachineddevice with in-situ cap according to this invention after packaging;

FIG. 6 is a view similar to FIG. 5 of an integrated circuit devicegenerally with an in-situ cap according to this invention; and

FIGS. 7A and B are a flow chart of a process according to thisinvention.

PREFERRED EMBODIMENT

There shown in FIG. 1 a micromachined switch device 10 which has beenfabricated in accordance with this invention as it appears just beforethe removal of the sacrificial layers within the in-situ cap which wasformed as a part of the basic processing of the integrated circuititself. The fabrication begins with the application of a silicon dioxidelayer 12 onto silicon substrate 14. A second layer 16 of silicon dioxideis laid down on layer 12 and is then masked to permit etching of theholes 18 in layer 16. After these holes are etched they are filled withaluminum to form conductors 20, 20′. These conductors function to makeelectrical interconnection between the micromachined element or otherintegrated circuit element inside of cap 22 and external circuits. Thethird silicon dioxide layer 24 is formed on layer 16. Layer 24 is nowmasked to expose holes 26, 28, 30 and 32 which are then formed byetching. After this another metal layer is deposited on layer 24 leavingexposed holes 26, 28, 30 and 32. This metal, such as Ru, (however anymetal which provides a low and stable resistance would be suitable), issputter deposited approximately 0.1 micron thick. This layer is maskedand etched, the mask is removed and the remaining Ru metal formscontacts to the under-lying Al metal 38, 48 and 50 and at the same timeforms the source 34, gate 36 and drain 38 of the micromachined elementand forms the anchors 42, 44 for the wall 46 of the cap. Also pads 48and 50 constitute the terminals to be wire bonded to external circuits.After this, a first sacrificial layer 52 is formed. Sacrificial layer 52is masked to create hole 70 approximately ⅓ the thickness of thesacrificial layer and then a deposit of a metal such as Ru, (however anymetal which provides a low and stable resistance would be suitable), ismade to fill the hole 70 to create tip contact 72. Sacrificial layer 52is masked again to expose holes communicating with Ru pads 34, 42, 44,48 and 56. A thin layer of Au e.g. 1.0 micron thick, is now formed onthese selected Ru pads, i.e. gold layers 60, 62, 64, 66 and 68. Layer 52is masked once again to expose the space for the beam 74 and for theanchor 76 of micromachined element, switch 40. A gold layer is depositedto create arm 74 and post 76 as shown, and then, a second sacrificiallayer 80 is added. Layer 80 is masked to create holes 82 which areetched right down to the gold layers 62 and 64. After this, layer 80 ismasked to create the top plate 86 of cap 22 and the gold is deposited tofill wall 45 and top 86 to complete the structure of cap 22. In thisparticular embodiment cap 22 is formed with a number of holes 90 whichserve to accept a release agent that is introduced through them torelease the sacrificial layers 52 and 80 inside of cap 22. The phraseintegrated circuit device or micromachined device refers generally tothe assembly 10 whereas the phrase integrated circuit element ormicromachined element refers to the things under the caps, e.g. switch40.

When this is done, the complete device appears as in FIG. 2. This cavitycan now be sealed with an epoxy or a similar sealant in holes 90 or maybe left open. If switch 40, or another micromachined element or otherintegrated circuit element had optical portions one of more of holes 90could be used as an optical port and as a hole for accepting a releaseagent similar to hole 90. Alternatively, a hole 92 through substrate 14could be used as an optical access port and as a hole for accepting arelease agent similar to hole 90. Often the cavity 94 formed in cap 22is to contain a predetermined environment such as a vacuum or an inertgas or a dielectric liquid to assist or enhance the operation of theswitch or other micromachined device or integrated circuit deviceprotected and isolated by cap 22. If this is the case, it may be desiredto seal hole 90 to keep in the fluid or seal the vacuum. In some casesthe holes may be simply made small enough so that the surface tension ofthe liquid prevents leakage or evaporation. Alternatively a reactiveliquid can be used, for example, such material can polymerize to a highmolecular weight material or crosslink into a gel or solid form: suchproducts would not leak out through the hole. Examples would includereactive silicone gels, epoxies, protein/water solutions. Alternativelya fluid can be introduced which modifies a surface in the cap such as asurface of the cap or of the micromachined device to reduce stictioh,passivate or impart some specific chemical reactivity on the surfaces(biological applications). For example, HMDS (Hexamethyldisilazane) canbe vapor deposited for reducing stiction. If the integrated circuitelement is not a device that needs to be free to move the sacrificiallayer may not need to be removed. In fact it may be beneficial to keepit there if, for example, it has optical or electrical or thermalinsulating properties that are desirable and a coefficient of expansionthat is compatible or just for support.

In another embodiment switch 40 a, FIG. 3, may be fabricated as a doublethrow switch by forming another contact tip 100 and another counter gateelectrode 102 directly on cap 22 a. In this case, another step isinserted before the cap is formed. In this step, layer 80 a is masked toprovide the holes 104, 106, in which the Ru can be deposited to createtip contact 100 and counter gate electrode 102. Then the required stepsare performed to create cap 22 a. After removal of the sacrificiallayers the device appears as shown in FIG. 4 as a fully operablemicromachined double throw switch.

Typically, device 10 or 10 a is die attached at 110, FIG. 5, to a paddleor lead frame 112 whose contacts 114, 116 are wire bonded to contacts 66and 68 with the entire device packaged in housing 120. As indicatedpreviously, the cap and the method of fabricating it is not limited tomicromachined devices, but is equally applicable to other types ofintegrated circuit devices as shown in FIG. 6 where instead of switch40, an integrated circuit element 122 such as an ASIC, microprocessor orthe like has been encapsulated by cap 22. In this particular case thepurpose of the cap instead of just protection or isolation may have beenalternatively or in addition to provide a Faraday cage by providing forexample a metallized outer layer 124 and grounding it as at 126 toprovide shielding.

The method for creating the devices of FIGS. 1 and 2 and FIGS. 3 and 4is shown in flow chart form in FIGS. 7A and B beginning with depositingthe first insulator, such as silicon dioxide, step 150, depositing thesecond silicon dioxide layer 152, and then masking the second layer tocreate holes and deposit, mask and etch a conductor layer, step 154. Thethird silicon dioxide layer is deposited and etched to create holes forthe Ru to contact the conductor pads 26, 28, 30, 32, step 156. A metalsuch as Ru (however any metal which provides a low and stable resistancewould be suitable), is deposited, masked and etched to form 34, 36, 38,42, 44, 48 and 50, step 158. Then the first sacrificial layer 52 isdeposited, step 160. The first sacrificial layer is masked and etched tocreate tip contact 72, and masked and etched a second time to create theholes for the beam anchor 34, cap anchors 42 and 44 and terminals 48, 50in step 162. The sacrificial layer is masked again and the Au isdeposited to form the beam 74, 76, terminal pads 66, 68 and the wallanchors 62, 64, steps 164 and 168. The second sacrificial layer is thendeposited 80, step 170, and then masked and etched to create holes anddeposit the wall 46, and the top of the cap 22 in step 172. Finally arelease agent is applied to remove the second and first sacrificiallayers, step 174. In the construction of FIGS. 3 and 4, the additionalsteps are added of; masking and etching the second sacrificial layer 80to form an upper tip 100 and counter electrode 102, step 176; thendepositing a metal such as Ru, (however any metal which provides a lowand stable resistance would be suitable) masking and etching to definethe tip 104 and counter electrode 106, step 178; this would be donebetween steps 170 and 172.

Further details of the method for creating the device of FIGS. 1 and 2is shown in chart A and for FIGS. 3 and 4 is shown in chart B.

CHART A Process Flow for Switch with the In-Situ Cap Basic SwitchProcess Sputter Deposit Ru Metal 0.1 um Thick Photolithography Metal-1Defines Source, Gate, Drain and Cap anchors Ion Beam Etch Metal-1 StripPhotoresist Sputter Deposit TiW/Cu 0.03 um/0.6 um Photolithography Tip-1Defines Tip-1 Diameter and Depth Ion Beam Etch Tip-1 0.3 um StripPhotoresist Sputter Deposit TiW/Ru 0.09 um/0.1 um Photolithography Tip-2Defines Ru Tip Ion Beam Etch Ru Strip Photoresist Photolithography BaseCut Defines beam anchors and cap anchors Ion Beam Etch Base StripPhotoresist Sputter deposit Au/TiW seed 0.1 um/0.03 um PhotolithographyInterconnect Defines Interconnect, Bond Pads, Cap Anchor Au PlateInterconnect 2.0 um Strip Photoresist Photolithography Beam Defines BeamAu Plate Beam 5-20 um depends on device Strip Photoresist Add In-SituCap Photolithography Cu Plate Defines Cu Spacer layer Plate Cu 1.0 umSputter Deposit TiW 0.03 um Strip Photoresist Photolithography CapDefines Cap Au Plate Cap 3.0 um Strip Photoresist Release Cap and Beamintroduce fill fluid Etch TiW 95% H₂O₂/5% NH₄OH 15 minutes Etch Cap Cu75% DIH₂O/25% HNO₃ 60 minutes Etch TiW 95% H₂O₂/5% NH₄OH 15 minutes EtchCu 75% DIH₂O/25% HNO₃ 60 minutes Etch TiW 95% H₂O₂/5% NH₄OH 15 minutesEvacuate With Vacuum Introduce Fill Fluid Photolithography Cap SealDefines Photoresist over Cap holes

CHART B Process Flow for the In-Situ Cap with Counter Gate Electrode andUpper Tip Basic Switch Process Sputter Deposit Ru Metal 0.1 um ThickPhotolithography Metal-1 Defines Source, Gate, Drain and Cap anchors IonBeam Etch Metal-1 Strip Photoresist Sputter Deposit TiW/Cu 0.03 um/0.6um Photolithography Tip-1 Defines Tip-1 Diameter and Depth Ion Beam EtchTip-1 0.3 um Strip Photoresist Sputter Deposit TiW/Ru 0.09 um/0.1 umPhotolithography Tip-2 Defines Ru Tip Ion Beam Etch Ru Strip PhotoresistPhotolithography Base Cut Defines beam anchors and cap anchors Ion BeamEtch Base Strip Photoresist Sputter deposit Au/TiW seed 0.1 um/0.03 umPhotolithography Interconnect Defines Interconnect, Bond Pads, CapAnchor Au Plate Interconnect 2.0 um Strip Photoresist PhotolithographyBeam Defines Beam Au Plate Beam 5-20 um depends on device StripPhotoresist Added Cap Process with gate counter electrode and 2^(nd) tipPhotolithography Cu Plate Defines Cu Spacer layer Plate Cu 1.0 um StripPhotoresist Sputter Deposit TiW 0.03 um Photolithography 2nd Tip Defines2^(nd) Tip Ion Beam Etch 0.3 um Strip Photoresist Sputter Deposit RuPhotolithography Metal-2 Defines Counter Gate electrode and 2^(nd) TipIon Beam Etch Metal-2 Strip Photoresist Sputter Deposit SiO2Photolithography Interconnect Oxide Defines Oxide over Ru to isolate Rufrom Cap Etch Oxide Strip photoresist Photolithography Cap Defines CapAu Plate Cap 3.0 um Strip Photoresist Release Cap and Beam introducefill fluid Etch TiW 95% H₂O₂/5% NH₄OH 15 minutes Etch Cap Cu 75%DIH₂O/25% HNO₃ 60 minutes Etch TiW 95% H₂O₂/5% NH₄OH 15 minutes Etch Cu75% DIH₂O/25% HNO₃ 60 minutes Etch TiW 95% H₂O₂/5% NH₄OH 15 minutesEvacuate With Vacuum Introduce Fill Fluid Photolithography Cap SealDefines Photoresist over Cap holes

Although specific features of the invention are shown in some drawingsand not in others, this is for convenience only as each feature may becombined with any or all of the other features in accordance with theinvention. The words “including”, “comprising”, “having”, and “with” asused herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments.

Other embodiments will occur to those skilled in the art and are withinthe following claims:

What is claimed is:
 1. A method of fabricating an in-situ cap for amicromachined device comprising: fabricating a micromachined element ona substrate with a sacrificial support layer intact; fabricating a capsacrificial support layer over said micromachined element; forming a capstructure in said sacrificial support layers covering said micromachinedelement; and removing the sacrificial support layers within said capstructure to release said micromachined element leaving an in-situ capintegrated with the element.
 2. The method of claim 1 in which formingsaid cap structure includes forming a cap hole around said element. 3.The method of claim 2 in which forming said cap structure includesfilling said cap hole to form a cap wall and covering said sacrificialsupport layers to form a top connected with said cap wall.
 4. The methodof claim 1 in which said cap is formed with at least one hole.
 5. Themethod of claim 4 in which removing the sacrificial support layersincludes introducing a release agent through said at least one hole insaid cap.
 6. The method of claim 4 in which said substrate is formedwith at least one hole.
 7. The method of claim 6 in which removing thesacrificial support layers includes introducing a release agent throughsaid at least one hole in said substrate.
 8. The method of claim 4 inwhich the cap hole is closed to seal the cap.
 9. The method of claim 4in which a fluid filler is introduced through the at least one hole insaid cap surrounding the micromachined element.
 10. The method of claim6 in which the cap hole is closed to seal the cap.
 11. The method ofclaim 6 in which a fluid filler is introduced through the at least onehole in said cap surrounding the micromachined element.
 12. The methodof claim 9 in which said cap hole is closed to seal in the fluid. 13.The method of claim 9 in which said cap hole is small and the surfacetension of the fluid prevents its escape.
 14. The method of claim 1 inwhich fabricating a cap includes forming a contact tip on said cap. 15.The method of claim 14 in which said micromachined element includes aswitch and said contact tip is a terminal of said switch.
 16. The methodof claim 15 in which fabricating a cap includes forming a gate electrodeon said cap for operating said switch.
 17. A method of fabricating anin-situ cap for an integrated circuit element comprising: fabricating anintegrated circuit element on a substrate; forming a support layer oversaid integrated circuit element; and forming a cap structure in saidsupport layer covering said integrated circuit element.
 18. The methodof claim 17 further including removing the support layer within said capstructure.
 19. The method of claim 17 in which forming said capstructure includes forming a cap hole around said element.
 20. Themethod of claim 19 in which forming said cap structure includes fillingsaid cap hole to form a cap wall and covering said support layer to forma top connected with said cap wall.
 21. The method of claim 17 in whichsaid cap is formed with at least one hole and removing the support layerincludes introducing a release agent through said hole in said cap. 22.The method of claim 17 in which said substrate is formed with at leastone hole and removing the support layer includes introducing a releaseagent through said hole in said substrate.
 23. The method of claim 21 inwhich the cap hole is closed to seal the cap.
 24. The method of claim 21in which a fluid filler is introduced through the cap hole into the capsurrounding the micromachined device.
 25. The method of claim 24 inwhich said cap hole is closed to seal in the fluid.
 26. The method ofclaim 24 in which the fluid is,a crosslinkable material.
 27. The methodof claim 21 in which a gas is introduced through the cap hole into thecap to modify at least one surface inside the cap.
 28. The method ofclaim 24 in which said cap hole is small and the surface tension of thefluid prevents its escape.
 29. The method of claim 17 in whichfabricating a cap includes forming a contact tip on said cap.
 30. Themethod of claim 29 in which said integrated circuit element includes aswitch and said contact tip is a terminal of said switch.
 31. The methodof claim 30 in which fabricating a cap includes forming a gate electrodeon said cap for operating said switch.